Promoted reduction of aromatic nitrogen compounds



United States PROMOTED REDUCTFON F AROMATIC NITRQGEN CGMPQUNDS Leigh C.Anderson, Ann Arbor, Micln, and Chester E.

Smith, Jr., Wilmington, Del., assignors to Allied Chernical & DyeCorporation, New York, N. Y., a corporation of New York No Drawing.Application August 18, 1954, Serial No. 450,784

11 Claims. (Cl. 260-143) This invention relates to improvements in themethod of reducing aromatic nitrogen compounds containing nitrogen in areducible form as a substitute of a benzene nucleus (that is, as asubstituent of a hydrogen atom forming part of a benzene nucleus) and ata higher stage, of oxidation than the hydrazo stage by the action ofmetal alcoholates. It relates more particularly to improvements in suchmethods, and especially in processes in which the reducing agent is analkali metal alcoholate, especially an alkali metal methylate andpreferably methanol and sodium hydroxide, whereby the reduction ispromoted.

Ordinarily, the reduction of nitrobenzene and related aromatic nitrocompounds by means of alkali metal alcoholates is carried out by heatingit with alcoholic caustic alkali (e. g., sodium hydroxide and a loweralcohol, usually methanol) at the boiling point of the mixture whilerefluxing at atmospheric pressure. Under these conditions, the alkalimetal alcoholates are not sufficiently strong reducing agents to carrythe reduction beyond the azoxy stage. As disclosed in U. S. Patents2,645,636 and 2,684,358, and in application Serial No. 290,089, filedMay 26, 1952, of Francis W. Cashion now U. S. Patent 2,765,301, thisreduction can be promoted, so as to result in the formation of reductionproducts of a lower stage of oxidation than the azoxy stage, or toobtain other beneficial results, by including in the reduction reactionmixtures naphthoquinoid compounds and especially naphthoquinones andaddition products thereof (for example, with bisulfites, heavy metalsalts, sulfiding agents, etc.), and quinoid hydroxynaphthalenecompounds.

The primary object of the present invention is to provide additionalreduction promoters which, when added to reduction reaction mixtures ofthe type referred to above, will eliect a similar reduction promotingeffect.

A further object of the present invention is to provide improvements inreductions of the type referred to above whereby the reducing power ofmetal alcoholate reducing agents and especially of alcoholic causticalkali reducing agents is enhanced and other advantages are secured.

Other objects of the present invention are to provide a process for theproduction of aromatic azo compounds in good yields by the reduction ofaromatic nitro compounds, and their reduction products up to andincluding azoxy compounds, with metal alcoholates under moderatereaction conditions and in simple apparatus; to provide a process forthe production of aromatic hydrazo compounds by reduction of aromaticnitro compounds and other reducible aromatic nitrogen compounds withmetal alcoholates under moderate conditions and in simple apparatus; andto provide improvements in the reduction of educible aromatic nitrogencompounds with metal alcoholates whereby the evolution of hydrogen gasduring the reduction is suppressed.

Additional objects in part will be obvious and in part will appearhereinafter.

According to the present invention the foregoing ob- 2,84,453 PatentedAug. 27, 1957 jects are accomplished and other benefits are secured bycarrying out the reduction of the reducible aromatic nitrogen compoundby means of a metal alcoholate in a reaction mixture in which one ormore reduction promoters of a special class have been incorporated.

The class of reduction promoters employed in accordance with the presentinvention is constituted of certain derivatives of benzoquinone, hereindesignated by the expression ortho-cycloalkano-benzoquinoid compounds.It consists of (1) benzoquinones in which two adjacent carbon atoms ofthe quinone nucleus other than those forming part of the carbonyl groupsare linked respectively to the end carbon atoms of a chain of at least 3carbon atoms, and preferably 4 carbon atoms, of which at least 2 aresaturated carbon atoms and the others may be unsaturated, hereindesignated by the expression "ortho-cycloalkano-benzoquinones (whetherfree from other substituents in the benzene nucleus besides the carbonyloxygen atoms and the cycloalkano radical, or containing additionalsubstituents in the benzene nucleus and/ or in the cycloalkano radical,wherein one or more of the hydrogen atoms is substituted by another atomor radicalfor example, halogen, hydroxyl, nitro, mercapto, amino, cyano,sulfo, carboxyl, alkyl, alkoxy etc.); (2) addition compounds of suchbenzoquinones (for example, with hydroquinones, bisulfites, heavy metalsalts, sulfiding agents, etc); (3) functional derivatives and tautomericforms of such benzoquinones capable of isomerizing to such benzoquinones(for example, imides, oximes, semicarbazones and hydrazones); and (4)hydroquinones corresponding to such benzoquinones, herein designatedortho-cycloalkano-benzohydroquinones.

Thus, said class of ortho-cycloalkano-benzoquinoid compounds includes:

2,3-cyclopropano-1,4-benzoquinone (4,7-indandione)2,3-cyclobuteno-1,4-benzoquinone (5,8-dihydro-1,4-naphthoquinone)2,3-cyclobutano-l,4-benzoquinone (5,6,7,8-tetrahydro-1,4-

naphthoquinone) 2,3-cyclobutano-1,4-benzoquinone oxime (4-nitroso-5,6,

7,8-tetrahydro-1-naphthol) 2,3-cyclobutano-1,4-benzoquinonebis-chlorimide (5,6,7,

8-tetrahydro-1,4-naphthoquinone bis-chlorimide)6-chloro-2,3-cyclobutano-1,4-benzoquinone5-chloro-6-anilino2,3-cyclobutano-1,4-benzoquinone5,6-dichlor-2,3-cyclobutano-l,4-benzoquinone5,6-dimethyl-2,3-cyclobutano-1,4-benzoquinone2,3-cyclobutano-1,4-benzoquinhydrone (5,6,7,8tetrahydro-l,4-naphthoquinhydrone) Sodium bisulfite addition product of2,3-cyclobutano-1,4- benzoquinone (cf. Example 4 of U. S. P. 2,645,636)Sodium hyd-rosulfide addition product of 2,3-cyclobutano-1,4-benzoquinone 2,3(2-chloro-cyclobuteno)1,4benzoquinone (6-chloro- 5,S-dihydro-l,4-naphthoquinone) 2,3-cyclobuteno-1,4-benzohydroquinone(5,8-dihydro-1,4-

naphthalenediol) 2,3-cyclobutano-1,2-benzohydroquinone(5,6,7,8-tetrahydro-l,2-naphthalenediol)2,3-cyclobutano-1,4-benzohydroquinone(5,6,7,8-tetrahydro1,4-naphthalenediol)2,3-cyclobutano-1,4-benzohydroquinone diacetatediacetoxy-S,6,7,S-tetrahydronaphthalene) 6-amino 2,3 cyclobutano 1,4benzohydroquinone (2- amino-5,6,7,8-tetrahydro-1,4-naphthalenediol)2,3-(2'-chloro-cyclobuteno) 1,4 benzohydroquinone (6-chloro-5,8-dihydro-1,4-naphthalenediol)6-methyl-2,3-cyclobuteno-1,4-benzohydroquinone (5,8-di

hydro-2-methyl-1,4-naphthalenediol) 2,3-(1',4'-ethano-cyclobuteno) 1,4benzohydroquinone (5,8-dihydro-5,8-ethano-1,4-naphthalenediol)6-methyl(2.,3'-dirnethyl-cyclobuteno) 1,4 benzohydroquinone (5,8 dihydro2,6,7 trimethyl-1,4-naphthalenediol).

Preferred ortho-cycloalkano-benzoquinoid compounds.

employed in accordance with the present invention are those in which thebenzoquinone and benzohydroquinone contain the carbonyl or hydroxylradicals in para relation (2,3-cycloalkano 1,4 benzoquinones andbenzohydroquinones). Those in which the cycloalkyl radical contains 4carbon atoms and the quinone nucleus is otherwise unsubstituted areespecially preferred. We have discovered that theortho-cycloalkano-benzoquinoid compounds constitute highlyetfectivereduction promoters in the reduction of aromatic nitrogencompounds of the type referred to above by metal alcoholates andespecially alkali metal alcoholates. We have found that the inclusion inthe reaction mixture of even a small amount of a benzoquinoid compoundof said type and especially of a 2,3-cyclo-alkano4,4-benzoquinone orcorresponding hydroquinone has a modifying effect upon the reaction as aresult of which a number of benefits may be secured.

Thus, as compared with a reduction carried out under the same conditionsbut in the absence of such reduction promoter, the speed of thereduction is increased and/or products of a higher stage of reductionare obtained, without substantial sacrifice of the total yield ofreduction products secured from the starting material. In the reductionof aromatic nitro compounds, the inclusion of a reduction promoter ofthe above type in the metal alcoholate reaction mixture makes possiblethe obtainment of azo compounds directly, without requiring the use ofdrastic operating conditions, such as high temperatures and pressures of10 or more atmospheres. Similarly, the inclusion of a reduction promoterof the above type in the reaction mixture makes possible the productionof hydrazo compounds from nitro, azoxy and azo compounds by means ofmetal alcoholate reducing agents Without requiring the use of drasticoperatingconditions. By their presence, .the reduction promoterssuppress almost completely side reactions leading to the evolution ofhydrogen gas during the reduction, thereby greatly increasing the safetyof the reduction process and minimizing waste of the reducing agent.

When no substantial change in the degree of reduction is desired, theinclusion of a reduction promoter of the above type in the reductionreaction medium makes possible the use of milder reaction conditions orthe use of decreased amounts of reducing agent. Thus, in the reductionof an aromatic nitro compound with sodium hydroxide and methyl alcohol,the presence of a reduction promoter of the above type in the reactionmixture makes possible the use of a lesser amount of sodium hydroxide,thereby decreasing the cost of the operation. This result is surprisingbecause the related alkyl-substituted benzoquinones do not display asimilar reduction-promoting eifect. For example, duroquinone(2,3,5,6-tetramethyl- 1,4-benzoquinone) and 2,3-dimethyl1,4-benzoquinone which might be expected to have a reduction-promotingeifect similar to that of 1,4-naphthoquinone, not only because of theirsimilar chemical composition to 1,4-naphthoquinone but the similarity oftheir oxidation-reduction potentials to that of 1,4-naphthoquinone, havevery little ,elfect upon the reduction reaction.

In the practice of the present invention, the reducible aromaticnitrogen compound is subjected to the reducing action of a metalalcoholate reducing agent in a reaction mixture in which one or more ofthe promoters referred calcium chloride in an oven at about 100.

to above have been incorporated. In the preferred practice of theinvention, wherein the reducible aromatic nitrogen compound is heatedwith a caustic alkali and an alcohol (preferably sodium hydroxide andmethanol) at the boiling point of the reaction mixture, the reductionpromoter is preferably mixed with the alcohol and, after adding thecaustic alkali" and heating, the nitrogen compound tion promoter may beadded to the reaction mixture in.

various ways and at various times, however, without departing from thescope of the invention.

The reduction promoter can be employed in various amounts. It is afeature of the present invention that merely small amounts of theortho-cycloalkano-benzoquinoid compounds are effective as reductionpromoters. Thus, amounts lying within the range 10, to & mol of suchbenzoquinoid compounds per mol of reducible aromatic nitrogen compoundare ordinarily employed. The minimum amount required to produce asignificant reduction-promoting etfect varies with the individualbenzoquinoid compound employed, the nature of the reducible aromaticnitrogen compound, and the reaction conditions. In general, a greaterreduction-promoting effect is secured by increasing the amount ofreduction promoter employed and a lesser effect results from decreasingthe amount employed, other reaction conditions being constant. Amountsgreater than V mol of reduction promoter per mol of reducible aromaticnitrogen compound usually are not advantageous, although they may beused if desired, since the additional benefits derived therefrom are notof sufficient commercial importance .to compensate for the increasedcost of the extra amount of reduction promoter.

The invention will be illustrated by the following specific examples,but it is to be understood that it is not limited to the details thereofand that changes may be made without departing from the scope of theinvention. The temperatures are in degrees centigrade and the parts areby weight, unless designated as parts by volume in which case the amountsignifies the volume occupied by the same number of parts by weight ofwater at 4 C.

Example 1 Part 1.Sixty parts of methanol and 0.95 part of5,6,7,8-tetrahydro-1,4-naphthoquinone were charged to a flask equippedwith a reflux condenser, agitator, dropping funnel and thermometer; then74.5 parts of solid sodium hydroxide were added, and the mixture washeated to refluxing. To the resulting heated mixture, 123 parts ofnitrobenzene were added over the course of an hour, and the reactionmass was then boiled under reflux for 22 hours under atmosphericpressure. A negligible amount of gaseous hydrogen was evolved during theaddition of nitrobenzene and the subsequent reflux period. The mixturewas then diluted with 300 parts of water and distilled (to removeunreacted methanol) until its temperature reached 110. The residue wasallowed to stand and separate into an upper oil phase containing thereduction product and a lower aqueous phase. The aqueous phase,consisting essentially of sodium hydroxide and sodium formate insolution, was drawn off at about The oil phase was boiled with dilutehydrochloric acid, and then allowed to stand. The oil phase whichseparated was drawn off, filtered hot, and dried over The yield ofproduct, which consisted essentially of a mixture of about 97% ofazobenzene and about 3% of azoxybenzene and had a setting point of 65.1,was about 98% of the theoretical based on the nitrobenzene charged.

Part 2.-The process of part 1 of this example was repeated without theaddition of 5,6,7,8-tetrahydro-l,4- naphthoquinonebut in otherwise thesame manner. A large amount of hydrogen was evolved and the productconsisted essentially of azoxybenzene (it had a setting point of 33.5").The yield was about 98% of. the theoretical.

Part 3.The process of part 1 of this example was repeated with 1.0 partof duroquinone (2,3,5,6-tetramethyl-1,4-benzoqu-inone) in place of the5,6,7,8-tetrahydro-lA-naphthoquinone, but in. otherwise the same manner.The product consisted essentially of a mixture of about 92% azoxybenzeneand about 8% azobenzene (it had a setting point of 312). The yield wasabout 98% of the theoretical.

Part 4.-The process of part 1 of this example was repeated with 1.0 partof 1,2,3,4,5,6,7,8-octahydro-9,10- anthraquinone in place of the5,6,7,8-tetrahydro-1,4- naphthoquinone, but in otherwise the samemanner. The product consisted essentially of a mixture of about 86%azoxybenzene and about 14% azobenzene. The yield was about 98% of thetheoretical.

Example 2 The procedure described in Example 1, part 1, was repeated,except that 0.9 part of sodium bisulfite was added to the flask inaddition to the 5,6,7,8-tetrahydro- 1,4-naphthoquinone and methanol, andthe mixture was refluxed for a half hour (to form the sodium bisulfiteaddition product of 5,6,7,8-tetrahydro-1,4-naphthoquinone) and thencooled to room temperature, before adding the sodium hydroxide. Theproduct consisted essentially of a mixture of about 82% azobenzene and18% azoxybenzene (it had a setting point of 594). The yield was about98% of the theoretical.

Example 3 The procedure described in Example 1, part 1, was repeated,except that 2.0 parts of 5,6,7,8-tetrahydro1,4- naphthoquinone wereemployed. The isolated oil phase was agitated with hot Water, afterwhich the aqueous mixture was cooled to room temperature and filtered,and the filter cake was dried. It consisted essentially of a mixture ofabout 80% of azobenzene and about 20% of hydrazobenzene. The yield ofproduct was 98% of the theoretical.

Example 4 Forty-three parts of methanol and 1 part of one of thereduction promoters set out in the following Table 1 were charged to aflask equipped with a reflux condenser, stirrer, dropping funnel andthermometer.

TABLE 1 A. 2,3-cyclobuteno-1,4-benzohydroquinone (5,8-dihydro-1,4-naphthalenediol) B. 2,3-cyclobutano-1,4-benzohydroquinone(5,6,7,8-tetrahydrol,4-naphthalenediol) C. 1,4-naphthohydroquinone(1,4-naphthalenediol) Fifty-six parts of solid sodium hydroxide werethen added with cooling and the resulting mixture was heated torefluxing. Then 85 parts of nitrobenzene were introduced over the courseof a half hour while maintaining the mass at 95, and the reaction masswas boiled, and refluxed under atmospheric pressure (about 90 to 100)for 22 hours (including the period of nitrobenzene addition). Themixture was then diluted with water to, 3000 parts by volume, cooled toabout 10, and filtered, and the filter cake was dried (either in avacuum drier at a temperature not exceeding 50 or by standing in theatmosphere at room temperature-2530).

The proportions of hydrazobenzene, azobenzene, azoxybenzene, and anilinethus produced are set out in Table 2.

TABLE 2 Percent of Theoretical Yield Based on Nitrobenzene ChargedPromoter Azobenzene Hydrazo- Aniline Azoxybenzene benzene None (Control)A 5 7 can be made without departing from the scope of the invention.

Thus, the process is applicable to the reduction of other aromaticnitrogen compounds containing nitrogen in a reducible form as asubstituent of a benzene nucleus, as for example, o-nitrotoluene,m-nitrotoluene, o-nitrochlorobenzene, m-nitrochlorobenzene,p-nitrophenetole, p-nitrobenzoic acid, o-nitrobenzene sulfonic acid, andtheir reduction products. In view of the extensive use of hydrazobenzeneand its o-substituted derivatives (such as 0,0-dichlorohydrazobenzene,o,o-hydrazotoluene, o,o-hydrazoanis0le, o,o'-diethoxy-hydrazobenzene,etc.) as intermediates for the manufacture of benzidine and relatedderivatives of benzidine, the process of the present invention is ofspecial value as a means for reducing the cost of manufacturing suchhydrazo compounds from the corresponding reducible aromatic nitrogencompounds (such as, nitrobenzene and its o-substituted derivatives andreduction products thereof) in which the nitrogen is at a higher stageof oxidation than the hydrazo stage.

The reduction of aromatic nitro compounds to azoxy compounds (1), ofazoxy compounds to azo compounds (2), and of azo compounds to hydrazocompounds (3) proceeds according to the following equations, in which Ris an aromatic nucleus:

In carrying out the reduction by means of sodium hydroxide and methanol,it is preferable to employ these reagents in amounts in excess of thosetheoretically required. Extra methanol over that theoretically requiredis generally desirable for use as a solvent, and an additional excess isdesirable to counteract the diluting effect of the water generated inaccordance with above Equations 1 and 2, which would otherwise tend toretard the reaction. An excess of sodium hydroxide also is desirablesince it tends to increase the rate of reaction.

It is possible to carry the reduction of a particular reducible aromaticnitrogen compound to various stages, depending upon the amounts ofsodium hydroxide and methanol employed, as well as the nature and amountof the particular promoter employed. Thus, it is possible to reducenitrobenzene to hydrazobenzene in a single reaction mixture. However, itis possible to reduce nitro benzene to azoxyand%or azobenzene in onereaction mixture, as illustrated in the above examples, and then toisolate and reduce the resulting azoxybenzene and/or azobenzene tohydrazobenzene with a fresh charge of sodium hydroxide and methanol.

The temperature at which the reaction is carried out also may be variedalthough, in the reduction performed with the aid of alcoholic causticalkali, temperatures at or near the boiling point of the reactionmixture at atmospheric pressure (ordinarily about to are preferred. Atlower temperatures, the reaction is slower, under otherwise similarconditions, and may require an excessively long time to produce the sameresults as the preferred temperatures. Conversely, higher reactiontemperatures result in a short time cycle but require the use of closedreaction vessels. However, temperatures greatly exceeding though notprecluded, are less desirable; since even in the presence of thereduction promoters they lead to evolution of considerable amounts ofhydrogen gas and formation of primary amines, with consequent loss ofyield of the desired reduction products.

While for economical and simple operation it is pre- 75 ferred to use,as a solvent or diluent of the reaction mixture, an excess of thealcohol employed for the alcoholate, the invention is not limitedthereto. Thus, other solvents and diluents can be employed; for example,the process may be carried out with amounts of sodium hydroxide andmethanol only slightly in excess over the amounts theoretically requiredfor the reduction, in a reaction medium containing a suflicient amountof xylene or other inert solvent or diluent (such as, benzene, toluene,monoand dichloro-benzenes) to provide a stirrable reaction mass.Further, while it is simpler to employ as the solvent or diluent anexcess of the alcohol functioning as a reducing agent, other alcoholscan be employed; also mixtures of alcohols can be used, especially whereit is desired to modify the boiling temperature of the reaction mixture'As a matter of convenience and for economical opera tion, the process isgenerally carried out by forming a metal alcoholate in the reactionmixture; for example, by reacting caustic alkali with the alcohol. Ifdesired, however, preformed metal alcoholates may be employed asreducing agents, thereby avoiding the diluting eflfect of the waterformed as a by-product of the reaction of caustic alkali with thealcohol.

Sodium hydroxide and methanol are employed in the specific examples inview of their relatively lower cost and ready availability. Theinvention is not limited thereto, however, and other alkalis (forexample, potas sium hydroxide) and other alcohols (for example, ethylalcohol and the various propyl, butyl and higher alcohols) may beemployed, if desired.

Other compounds may be substituted forthe sodium bisulfite employed inExample 2 to form addition products with theortho-cycloalkano-benzoquinone. Thus, corresponding amounts of thevarious other bisulfites and other compounds disclosed in U. S. P.2,645,636, or of sodium hydrosulfide or the other sulfiding agentsdisclosed in application Serial No. 290,089, referred to above, may beemployed. The products of the reduction can be isolated from thereaction mixtures in any suitable manner. Aside from those cases inwhich the reaction mixture contains an insoluble residue resulting fromthe presence of the reduction promoter in the reaction mixture, theisolation of the reduction products can be carried out in the usualmanner. Thus, for example, the reaction mixture may be cooled tocrystallize the reduction product and filtered, and the cake washed withwater to remove alcohol, sodium formate formed as a by-product of thereduction, and sodium hydroxide. Generally, it is preferred to steamdistill the methanol (and dehydrate the aqueous methanol thus obtainedby fractional distillation for reuse in subsequent reactions), and thencool the remaining hot aqueous mass to crystallize the reductionproduct, which may be separated and washed with water as usual. Wherethe product is molten in the hot mixture, as in the case of azoxyandazobenzenes, it is simpler to stratify the mass into an aqueous phaseand an oil phase, whereupon the latter can be readily separated, asillustrated in the examples.

Ordinarily, the reduction promoters of the above type are soluble in theaqueous and/or alcoholic layer and are removed therewith from thereduction product, When the use of the reduction promoter produces asmall amount of insoluble by-product, it may be removed by filtering thehot mixture prior to the phase-separation, or in any other suitablemanner.

We claim:

l. The improvement in the method of reducing an aromatic nitrogencompound containing nitrogen in a reducible form as a substituent of abenzene nucleus at a higher stage-of oxidation than the hydrazo stage-bythe action of a metal alcoholate, which comprises carrying out thereduction in a reaction mixturein which an orthocycloalkano-benzoquinoidcompound has been incorporated, whereby the reduction of the aromaticnitrogen compound is promoted.

2. A method as defined in claim 1, wherein the alcoholate'is sodiummethylate, the aromatic nitrogen compound is reduced to a lower stage ofoxidation than the azoxy stage and the ortho-cycloalkano-benzoquinoidcompound is selected from the group consisting of,2,3-cycloalkano-1,4-benzoquinones having a hydrocarbon chainof 4 carbonatoms in the cycloalkano radical and the correspondingbenzohydroquinones.

3. A method as defined in claim 1 wherein the metal alcoholate is sodiummethylate, the aromatic nitrogen compound is reduced to a lower stage ofoxidation than the azoxy stage, and the ortho-cycloalkano-benzoquinoidcompound is an addition product of a 2,3-cycloa1kano-l,4- benzoquinonehaving a chain of 4 carbon atoms in the cycloalkano radical.

4. The improvement in the method of reducing a reducible aromaticnitrogen compound selected from the group consisting of nitrobenzene,its ortho-methyl, halogen, methoxy, ethoxy, carboxy and sulfoderivatives, and their reduction products in which the nitrogen is at ahigher stage of oxidation than the hydrazo stage, by the action of ametal alcoholate, which comprises reducing the aromatic nitrogencompound to a lower stage of oxidation than the azoxy stage by reactingthe aromatic nitrogen compound with a reducing mixture of an alkalimetal hydroxide and a lower alcohol in a reaction mixture in which asmall amount of an ortho-cycloalkanobenzoquinoid compound has beenincorporated.

5. A method as defined in claim 4, which comprises heating the aromaticnitrogen compound with a reducing mixture of sodium hydroxide andmethanol in a reaction mixture in which a2,3-cycloalkano-1,4-benzoquinone having a chain of 4 carbon atoms in thecycloalkyl radical has been incorporated.

6. A method as defined in claim 5, wherein a small amount of a2,3-cycloalkano-1,4-benzoquinone having a chain of 4 carbon atoms in thecycloalkyl radical is incorporated with the methanol, sodium hydroxideis added, and the aromatic nitrogen compound is heated with theresulting reaction. mixture.

7. A method as defined in claim 5, wherein the cycloalkano-benzoquinoneis 2,3-cyclobuteno-1,4-benzoquinone.

- 8. A method as defined in claim 5, wherein thecycloalkano-benzoquinone is 2,3-cyclobutano-l,4-benzoquinone.

9. A method as defined in claim 4, which comprises heating the aromaticnitrogen compound with a reducing mixture of sodium hydroxide andmethanol in a reaction mixture in which a2,3-cycl'oalkano-1,4-benzohydroquinone having a chain of 4 carbon atomsin the cycloalkyl radical has been incorporated.

10. A method as defined in claim 9, wherein thecycloalkano-benzohydroquinone is 2,3-cyclobuteno-1,4-benzohydroquinone.

11. A method as defined in claim 9, wherein thecycloalkano-benzohydroquinone is 2,3-cyclobutano-1,4-benzohydroquinone.

References Cited in the file of this patent UNITED STATES PATENTS SognJuly 20, 1954'

1. THE IMPROVEMENT IN THE METHOD OF REDUCING AN AROMATIC NITROGENCOMPOUND CONTAINING NITROGEN IN A REDUCIBLE FORM AS A SUBSTITUENT OF ABENZENE NUCLEUS AT A HIGHER STAGE OF OXIDATION THAN THE HYDRAZO STAGE BYTHE ACTION OF A METAL ALCOHOLATE, WHICH COMPRISES CARRYING OUT THEREDUCTION IN A REACTION MIXTURE IN WHICH ANORTHOCYCLOALKANO-BENZOQUINOID COMPOUND HAS BEEN INCORPORATED, WHEREBYTHE REDUCTION OF THE AROMATIC NITROGEN COMPOUND IS PROMOTED.